Search Options

Search form

Welcome to the National Climate Assessment

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

Introduction

Coasts covers the special challenges faced by the coastal areas of our nation, including the Great Lakes coasts as well as ocean coasts. The Highlights section below offers a high-level overview of climate change impacts on coastal areas, including the five Key Messages and selected topics. (see Ch. 25: Coasts)

Key Message: Coastal Lifelines at Risk

Coastal lifelines, such as water supply and energy infrastructure and evacuation routes, are increasingly vulnerable to higher sea levels and storm surges, inland flooding, erosion, and other climate-related changes.

Key Message: Economic Disruption

Nationally important assets, such as ports, tourism, and fishing sites, in already-vulnerable coastal locations, are increasingly exposed to sea level rise and related hazards. This threatens to disrupt economic activity within coastal areas and the regions they serve and results in significant costs from protecting or moving these assets.

Key Message: Uneven Social Vulnerability

Socioeconomic disparities create uneven exposures and sensitivities to growing coastal risks and limit adaptation options for some coastal communities, resulting in the displacement of the most vulnerable people from coastal areas.

Key Message: Vulnerable Ecosystems

Coastal ecosystems are particularly vulnerable to climate change because many have already been dramatically altered by human stresses; climate change will result in further reduction or loss of the services that these ecosystems provide, including potentially irreversible impacts.

Key Message: The State of Coastal Adaptation

Leaders and residents of coastal regions are increasingly aware of the high vulnerability of coasts to climate change and are developing plans to prepare for potential impacts on citizens, businesses, and environmental assets. Significant institutional, political, social, and economic obstacles to implementing adaptation actions remain.

Coasts

More than 50% of Americans – 164 million people – live in coastal counties, with 1.2 million added each year. Residents, combined with the more than 180 million tourists that flock to the coasts each year,1,2 place heavy demands on the unique natural systems and resources that make coastal areas so attractive and productive.1,2

No other region concentrates so many people and so much economic activity on so little land, while also being so relentlessly affected by the sometimes violent interactions of land, sea, and air. Humans have heavily altered the coastal environment through development, changes in land use, and overexploitation of resources.

Now, the changing climate is imposing additional stresses,3 making life on the coast more challenging. The consequences will ripple through the entire nation.

Lifelines at Risk

Paths of Hurricanes Katrina and Rita Relative to Oil and Gas Production Facilities

A substantial portion of U.S. energy facilities are located on the Gulf Coast as well as offshore in the Gulf of Mexico, where they are particularly vulnerable to hurricanes and other storms and sea level rise. (Figure source: U.S. Government Accountability Office 20064).

Key coastal vulnerabilities arise from complex interactions among climate change and other physical, human, and ecological factors. These vulnerabilities have the potential to fundamentally alter life at the coast and disrupt coast-dependent economic activities.

The more than 60,000 miles of coastal roads are essential for human activities. Already, many coastal roads are affected during storm events5,6,7,8 and extreme high tides.9,10,11,12 As coastal bridges, tunnels, and roads are built or redesigned, engineers must account for present and future climate change impacts.13

Wastewater management and drainage systems are also at risk. Systems will become overwhelmed with increased rainfall intensity over more impervious surfaces, such as asphalt and concrete.14,15,16,17,18,19,20 Sea level rise will cause a variety of problems including salt water intrusion into coastal aquifers.21,22,23 Together, climate change impacts increase the risks of urban flooding, combined sewer overflows, deteriorating coastal water quality, and human health impacts.24,25,26

Natural gas platform in the Gulf of Mexico illustrates some of the infrastructure at risk from coastal storms.

The nation’s energy infrastructure, such as power plants, oil and gas refineries, storage tanks, transformers, and electricity transmission lines, are often located directly in the coastal floodplain.27,28,29,30 Roughly two-thirds of imported oil enters the U.S. through Gulf of Mexico ports,31 and unless adaptive measures are taken, storm-related flooding, erosion, and permanent inundation from sea level rise will disrupt the supply of refined products to the rest of the nation.32,33,34,35,36

There are a variety of options to protect, replace, and redesign existing infrastructure, including flood proofing and flood protection through dikes, berms, pumps, integration of natural landscape features, elevation, more frequent upgrades, or relocation.37,38 Such adaptation options are best assessed in a site-specific context, weighing social, economic, and ecological considerations.

Economic Disruption

More than 5,790 square miles and more than $1 trillion of property and structures are at risk of inundation from sea level rise of two feet above current sea level – which could be reached by 2050 under a high rate of sea level rise, by 2070 assuming a lower rate of rise, and sooner in areas of rapid land subsidence.40,41,42 Roughly half of the vulnerable property value is located in Florida.41,43

Although comprehensive national estimates are not yet available, regional studies are indicative of the potential risk: the incremental annual damage of climate change to capital assets in the Gulf region alone could be $2.7 to $4.6 billion by 2030, and $8.3 to $13.2 billion by 2050; about 20% of these at-risk assets are in the oil and gas industry.44 Investing approximately $50 billion for adaptation over the next 20 years could lead to approximately $135 billion in averted losses over the lifetime of adaptive measures.44,45

Coastal recreation and tourism comprises the largest and fastest-growing sector of the U.S. service industry, accounting for 85% of the $700 billion annual tourism-related revenues.1,46,47 Hard shoreline protection against the encroaching sea (like building sea walls or riprap) generally aggravates erosion and beach loss, and causes negative effects on coastal ecosystems, undermining the attractiveness of beach tourism. Thus, “soft protection,” such as beach replenishment or conservation and restoration of sand dunes and wetlands, is increasingly preferred to “hard protection” measures.

Socioeconomic Disparities

There are large socioeconomic disparities in coastal areas,48,49,50,51,52,53 and a full understanding of risk for coastal communities requires consideration of social vulnerability factors that limit people’s ability to adapt. These factors include lower income, minority status, low educational achievement, advanced age, lower economic and social mobility, and much lower likelihood of being insured than wealthy property owners.54,55,56,57,58 The most socially vulnerable populations also tend to have fewer adaptation options in their current locations, and thus may be at greater risk of dislocation.51,59,60,61,62

Vulnerable Ecosystems

Coastal ecosystems provide a suite of valuable benefits (ecosystem services) on which humans depend, including reducing the impacts from floods, buffering from storm surge and waves, and providing nursery habitat for important fish and other species, water filtration, carbon storage, and opportunities for recreation and enjoyment.67,68,69,70,71

However, many of these ecosystems and the services they provide are rapidly being degraded by human impacts, including pollution, habitat destruction, and the spread of invasive species.

These existing stresses on coastal ecosystems will be exacerbated by climate change effects, such as increased ocean temperatures that lead to coral bleaching,72 altered river flows affecting the health of estuaries,73 and acidified waters threatening shellfish.74 Of particular concern is the potential for coastal ecosystems to cross thresholds of rapid change (“tipping points”), beyond which they exist in a dramatically altered state or are lost entirely from the area. Some ecosystems are already near tipping points and in some cases the changes will be irreversible.75

Adaptation Challenges and Opportunities

Coastal leaders and populations are increasingly concerned about climate-related impacts and are developing adaptation plans,76,77,78 but support for development restrictions or managed retreat is limited.79,80,81,82

Enacting measures that increase resilience in the face of current hazards, while reducing long-term risks due to climate change, continues to be challenging.83,84,85

A coastal ecosystem restoration project in New York City integrates revegetation (a form of green infrastructure) with bulkheads and riprap (gray or built infrastructure). Investments in coastal ecosystem conservation and restoration can protect coastal waterfronts and infrastructure, while providing additional benefits, such as habitat for commercial and recreational fish, birds, and other animal and plant species, that are not offered by built infrastructure.

A robust finding is that the cost of inaction is 4 to 10 times greater than the cost associated with preventive hazard mitigation.41,86 Even so, prioritizing expenditures now whose benefits accrue far in the future is difficult.87

Cumulative costs to the economy of responding to sea level rise and flooding events alone could be as high as $325 billion by 2100 for 4 feet of sea level rise, with $130 billion expected to be incurred in Florida and $88 billion in the North Atlantic region.42 The projected costs associated with one foot of sea level rise by 2100 are roughly $200 billion. These figures exclude losses of valuable ecosystem services, as well as indirect losses from business disruption, lost economic activity, impacts on economic growth, or other non-market losses.42,88,89,90

Property insurance can serve as an important mode of financial adaptation to climate risks,91 but the full potential of leveraging insurance rates and availability has not yet been realized.92,93,94 Federal fiscal exposure for the National Flood Insurance Program was estimated at nearly $1.3 trillion in 2012.95 Reforms were enacted in 2012, though various challenges remain.96,97,98,99,100,101

Climate adaptation efforts that integrate hazard mitigation, natural resource conservation, and restoration of coastal ecosystems can enhance ecological resilience and reduce the exposure of property, infrastructure, and economic activities to climate change impacts.69,102,103,104,105,106,107,108 Yet, the integration and translation of scientific understanding of the benefits provided by ecosystems into engineering design and hazard management remains challenging.109,110 Adaptation efforts to date that have begun to connect these issues across jurisdictional and departmental boundaries and create innovative solutions are thus extremely encouraging.92,111,112,113,114

Sea level has risen approximately 7 inches from 1900 to 2005, and is expected to rise at growing rates in this century.

Higher temperatures; changes in precipitation, runoff and water supplies; and saltwater intrusion into coastal aquifers will result in negative impacts on coastal water resources.

Coastal storm surges are expected to be higher due to increases in sea level alone, and more intense persistent storm tracks (atmospheric river systems) will increase coastal flooding risks from inland runoff.

The San Francisco Bay and San Joaquin/Sacramento River Delta are particularly vulnerable to sea level rise and changes in salinity, temperature, and runoff; endangering one of the ecological “jewels” of the West Coast, growing development, and crucial water infrastructure.

The substantial global sea level rise is regionally moderated by the continuing uplift of land, with few exceptions, such as the Seattle area and central Oregon.

Commercial shellfish populations are at risk from ocean acidification.

The region’s relatively high economic dependence on commercial fisheries makes it sensitive to climate change impacts on marine species and ecosystems and related coastal ecosystems.

Coastal storm surges are expected to be higher due to increases in sea level alone, and more intense persistent storm tracks (atmospheric river systems) will increase coastal flooding risks from inland runoff.

The number of land-falling tropical storms may decline, reducing important rainfall.

The incidence of harmful algal blooms is expected to increase with climate change, as are health problems previously uncommon in the region.

Adaptation Examples: Examples of Adaptation Activities in Coastal Areas of the U.S. and Affiliated Island States are compiled from technical input reports, the regional chapters in this report, and scientific literature. For related information, see data.globalchange.gov

Shoreline Erosion: Probability of Shoreline Erosion greater than 3.3 feet per year for counties along the coast. Probability is based on historical conditions only and does not reflect the possibility of acceleration due to increasing rates of sea level rise.63,64,65

Social Vulnerability: Social Vulnerabilty Index (SoVI) at the Census tract level for counties along the coast. The Social Vulnerability Index provides a quantitative, integrative measure for comparing the degree of vulnerability of human populations across the nation. A high SoVI (dark pink) typically indicates some combination of high exposure and high sensitivity to the effects of climate change and low capacity to deal with them. Specific index components and weighting are unique to each region (North Atlantic, South Atlantic, Gulf, Pacific, Great Lakes, Alaska, and Hawai‘i). All index components are constructed from readily available Census data and include measures of poverty, age, family structure, location (rural versus urban), foreign-born status, wealth, gender, Native American status, and occupation.51,66

Regional Differences: Regional threats from climate change are compiled from technical input reports, the regional chapters in this report, and from scientific literature. For related information, see data.globalchange.gov

Agyeman, J., P. Devine-Wright, and J. Prange, 2009: Close to the edge, down by the river? Joining up managed retreat and place attachment in a climate changed world. Environment and Planning A, 41, 509-513, doi:10.1068/a41301. URL | Detail↩

H. John Heinz III Center for Science Energy and the Environment, 2000: The Hidden Costs of Coastal Hazards: Implications for Risk Assessment and Mitigation. A multisector collaborative project of the H. John Heinz Center for Science, Economics, and the Environment. Island Press, 252 pp. | Detail↩

The World Bank, 2009: Convenient Solutions for an Inconvenient Truth: Ecosystem-based Approaches to Climate Change. The World Bank, The International Bank for Reconstruction and Development, 91 pp. URL | Detail↩

National Climate Assessment

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.